Overcoming the blood–brain barrier (BBB) remains a significant challenge with regard to drug delivery to the brain. By incorporating targeting ligands, and by carefully adjusting particle sizes, nanocarriers can be customized to improve drug delivery. Among these targeting ligands, transferrin stands out due to the high expression level of its receptor (i.e., transferrin receptor) on the BBB. Porous silicon nanoparticles (pSiNPs) are a promising drug nanocarrier to the brain due to their biodegradability, biocompatibility, and exceptional drug-loading capacity. However, an in-depth understanding of the optimal nanoparticle size and transferrin surface density, in order to maximize BBB penetration, is still lacking. To address this gap, a diverse library of pSiNPs was synthesized using bifunctional poly(ethylene glycol) linkers with methoxy or/and carboxyl terminal groups. These variations allowed us to explore different transferrin surface densities in addition to particle sizes. The effects of these parameters on the cellular association, uptake, and transcytosis in immortalized human brain microvascular endothelial cells (hCMEC/D3) were investigated using multiple in vitro systems of increasing degrees of complexity. These systems included the following: a 2D cell culture, a static Transwell model, and a dynamic BBB-on-a-chip model. Our results revealed the significant impact of both the ligand surface density and size of pSiNPs on their ability to penetrate the BBB, wherein intermediate-level transferrin densities and smaller pSiNPs exhibited the highest BBB transportation efficiency in vitro. Moreover, notable discrepancies emerged between the tested in vitro assays, further emphasizing the necessity of using more physiologically relevant assays, such as a microfluidic BBB-on-a-chip model, for nanocarrier testing and evaluation.

The blood–brain barrier (BBB) poses a formidable challenge to drug delivery to the brain. One promising approach involves receptor‐mediated transcytosis via Angiopep‐2 peptide (Ang‐2)‐conjugated nanoparticles. However, the influence of Ang‐2 density on BBB penetration remains poorly understood. We developed a versatile polymeric nanoparticle system with tunable Ang‐2 surface density and systematically examined its influence on BBB penetration through various in vitro assays and an in vivo study. The results reveal a nuanced relationship between ligand density and BBB penetration across experimental setups. In 2D cell culture, Ang‐2 density positively correlates with nanoparticle association in human cerebral microvascular endothelial cells (hCMEC/D3) with a distinctive inflection point. Conversely, in the Transwell model, higher Ang‐2 density negatively correlate with BBB penetration, while the BBB‐glioblastoma (GBM)‐on‐a‐chip shows the opposite trend. Disparities may be due to differences in avidity under static versus dynamic conditions, modulating nanoparticle interactions due to fluidic forces. In vivo studies align with the microfluidic model. Loading doxorubicin into the optimized nanoparticles achieves controlled pH‐responsive release and enhanced anticancer effects against U87 GBM cells in 2D cell cultures and a 3D BBB‐GBM‐on‐a‐chip. These results underscore the importance of optimizing Ang‐2 density for BBB penetration and emphasize the utility of dynamic models for the preclinical assessment of brain‐targeting nanoparticles.

Chronic pain is a global health issue that is poorly understood and challenging to treat. Improving pain classification and treatment requires new strategies that objectively discriminate between pain conditions and minimise subjectivity associated with the perception of pain. To address this, we have developed a microfluidic biosensor - termed 'pain-on-a-chip' - that leverages recent advancements in biocompatible microfluidic technology with on-chip differentiation of nociceptor-like cells, enabling small sample volumes to be used. Following neuronal differentiation, we used on-chip live cell Ca²⁺ imaging to functionally validate the system. This includes characterising excitation responses in cells challenged with microfluidic perfusion of known nociceptive stimuli and biological fluids collected from different preclinical pain models. Our results demonstrate that this platform has the potential to discriminate between serum samples from distinct chronic pain models. This system has potential as an objective, and minimally invasive method for distinguishing between different subtypes of chronic pain.

Microfluidic technology is applied across various research areas including organ-on-chip (OOC) systems. The main material used for microfluidics is polydimethylsiloxane (PDMS), a silicone elastomer material that is biocompatible, transparent, and easy to use for OOC systems with well-defined microstructures. However, PDMS-based OOC systems can absorb hydrophobic and small molecules, making it difficult and erroneous to make quantitative analytical assessments for such compounds. In this paper, we explore the use of a synthetic fluoropolymer, poly(4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene) (Teflon™ AF 2400), with excellent “non-stick” properties to functionalize OOC systems. Cannabinoids, including cannabidiol (CBD), are classes of hydrophobic compounds with a great potential for the treatment of anxiety, depression, pain, and cancer. By using CBD as a testing compound, we examined and systematically quantified CBD absorption into PDMS by means of an LC-MS/MS analysis. In comparison to the unmodified PDMS microchannels, an increase of approximately 30× in the CBD signal was detected with the fluoropolymer surface modification after 3 h of static incubation. Under perfusion conditions, we observed an increase of nearly 15× in the CBD signals from the surface-modified microchannels than from the unmodified microchannels. Furthermore, we also demonstrated that fluoropolymer-modified microchannels are compatible for culturing hCMEC/D3 endothelial cells and for CBD perfusion experiments.

Porous silicon nanoparticles (pSiNPs) represent a unique drug delivery candidate owing to the biocompatibility, degradability, high loading capacity as well as production scalability. Various endeavours have been reported to make practical formulations with pSiNPs. However, existing protocols still lack simplicity and sometimes stability in physiological environment. Herein, we report the use of stimuli-responsive poly(disulfide) as a sealing/coating strategy for pSiNPs. The polymer matrix was formed in one-pot protocols in water and various payloads, including small molecule drugs, drug conjugate and small interfering RNA (siRNA), could be loaded spontaneously. The engineered hybrid nanoparticles demonstrated excellent stability in saline and tuneable degradability. Drugs like doxorubicin (DOX) and camptothecin (CPT) were loaded physically by polymer entrapment, while disulfide-based self-immolative linker (SIL) were also used to covalently load CPT. To load macromolecular payload siRNA, we developed a polymerisable ionisable lipid (PIL) strategy to suit this sealing strategy. siRNA was loaded via electrostatic interactions followed by polymer entrapment. In vitro experiments revealed the successful delivery of therapeutic candidates in cells. These combined efforts provide a practical solution for the use of pSiNPs in drug delivery.